function show_tab(el)
{
	if(!el)
		el = document.getElementById('main_tab');
	var children = document.getElementById('tab-nav').getElementsByTagName('a');
	for ( var i in children )
	{
		children[i].className = "";
	} 
	el.className = "activeTab";
	
	var tabs = getElementsByClassName("tab");
	for ( var i in tabs)
	{
		tabs[i].style.display = "none";
	} 
	var tab = document.getElementById(el.getAttribute('rel'));
	tab.style.display = 'block';
}

function getElementsByClassName(classname) {
	var node = document.getElementById("tab-container");
	var a = [];
	var re = new RegExp('\\b' + classname + '\\b');
	var els = node.getElementsByTagName("*");
	for(var i=0,j=els.length; i<j; i++)
		if(re.test(els[i].className))a.push(els[i]);
	return a;
}